My invention relates to a squelch circuit for a radio receiver, and particularly to such a squelch circuit that provides fast or slow operation, depending upon the characteristics of the received frequency modulated signal.
Squelch circuits are used with frequency modulation (FM) radio receivers to eliminate noise that would be heard in the absence of a received FM signal. To eliminate as much noise as possible after an FM signal has terminated, a fast-acting squelch circuit is desirable. However, where a weak FM signal has terminated, or where an FM signal is subject to fading (particularly when received by or from a moving vehicle), noise is frequently already present so that a slow-acting squelch circuit is desirable.
Accordingly, a primary object of my invention is to provide a new and improved squelch circuit for a frequency modulation radio receiver.
Another object of my invention is to provide a new and improved squelch circuit that does not unsquelch a radio receiver for frequency modulated signals whose strength is below a predetermined level or magnitude.
Another object of my invention is to provide a new and improved squelch circuit that rapidly unsquelches a radio receiver upon receipt of a strong frequency modulated signal, and that rapidly squelches the receiver upon termination of a strong frequency modulated signal.
Another object of my invention is to provide a new and improved squelch circuit which operates relatively slowly when a relatively weak frequency modulated signal is terminated, thus improving the operation of the receiver.
Another object of my imvention is to provide a new and improved squelch circuit which operates slowly when a frequency modulated signal begins to fade, thus maintaining operation of the receiver during relatively normal conditions of fade, such as caused by operation of a moving vehicle or multiple propagation paths, such as caused by reflections.
Another and fairly specific object of my invention is to provide a new and improved squelch circuit for use with a frequency modulation radio receiver that operates with priority search lock monitor arrangements.